题解

#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,a = 2 ,b = 0;
	cin>>n;
	for(int i = 2 ; i <= n ; i++){
		b = a + 4 * i - 3; 
        a = b;
	} 
	cout << a;  //主要是思考过程，题解没什么好看的♂
	return 0;
}